Display devices utilizing liquid crystal compounds which are widely employed at present are usually driven by TN (twisted nematic) mode.
When the display device is driven by TN mode, however, the positions of liquid crystal compound molecules in the element of the device must be changed in order to change a displayed image. As a result, there are involved such problems that the driving time of the device becomes prolonged, and a voltage required for changing the positions of the liquid crystal compound molecules, namely, power consumption becomes large.
Switching elements using ferroelectric liquid crystal compounds, different from those in which TN mode or STN mode is utilized, are able to function only by changing the molecular orientation direction of the liquid crystal compounds, and hence the switching time is markedly shortened. Further, the value of Ps.times.E, which is obtained from a spontaneous polarization (Ps) of the ferroelectric liquid crystal compound and an intensity of the electric field (E), is an effective energy output for changing the molecular orientation direction of the liquid crystal compounds, and accordingly the power consumption is also significantly diminished. Such ferroelectric liquid crystal compounds as mentioned above have two stable states, namely, bistability, in accordance with the direction of the applied electric field, and therefore show significantly excellent switching threshold value characteristics. Accordingly, the ferroelectric liquid crystal compounds are particularly suitable for display devices for animations.
Antiferroelectric liquid crystals also have the above-mentioned excellent characteristics, and in addition, they show easy realization of memory and high contrast. Accordingly, the antiferroelectric liquid crystals are also particularly suitable for display devices.
As the antiferroelectric liquid crystals (also referred to as "AFLC" for short hereinafter), there have been so far reported a liquid crystal MHPOBC (abbreviation for [4-(1-methylheptyloxycarbonylphenyl)4'-octyloxybiphenyl-4'-carboxylate], etc.
However, the conventionally known antiferroelectric liquid crystals are insufficient in the orientation characteristics when practically used for display devices.
For enhancing the orientation characteristics of the aforementioned ferroelectric liquid crystal, molecules of the ferroelectric liquid crystal are arranged in such a manner that the liquid crystal is in a cholesteric phase on the high temperature side where the molecules can be freely orientated, and that the liquid crystal phase is changed to be Iso (liquid phase)-Ch (cholesteric phase)-SmC* (chiral smectic phase) as the temperature is changed from a high temperature to a low temperature to make the initial orientation directions of the molecules almost the same. As a result, high orientation of the ferroelectric liquid crystal molecules can be achieved.
As for the antiferroelectric liquid crystals (AFLC), however, no liquid crystal showing phase change of Iso-Ch-(SmA)-SmC.sub.A * (AFLC phase) in accordance with lowering of a temperature has been found yet.